From our independent research, we have determined that a need exists in the medical community for an instrument that is capable of accurately and continuously monitoring blood flow in vivo. We have designed a unique fiber optic sensor which can be used for such measurements in large and small arteries. This technique overcomes many of the disadvantages of current methods and provides the following major features. . Continuous measurement of blood flow, . accuracy . small size (can be made as small as .3mm diameter), . reliable and safe (non-thrombogenic), and . direct measurement and display of flow pulse shape (flow vs. time). The specific aim of this Phase I proposal is to build a prototype of the flow catheter and to validate its predicted performance under laboratory conditions. The commercial applications for the OPTECH disposable catheter is very promising. With more than one million cardiovascular procedures done annually and with more than 300,000 by-pass surgeries done annually, the continuous and accurate measurement features of the OPTECH catheter will find use in diagnostic procedures, critical care monitoring, during angioplastic procedures, and for continuous cardiac output monitoring. Satisfactory demonstration during Phase I will set the stage for commercialization of the product during Phase II.